The present invention relates to a surgical instrument commonly referred to as a trocar, or an obturator and cannula, often used in laparoscopic or arthroscopic surgery. More particularly, the invention relates to new and improved designs for shields, blade mountings and sheaths especially adapted for flat bladed trocars.
Many surgical procedures are now being performed with the use of trocars and cannulas. Originally these devices were used for making a puncture and leaving a tube to drain fluids. As technology and surgical techniques have advanced, it is now possible to insert surgical instruments through the cannulas and perform invasive procedures through openings less than half an inch in diameter. Previously these procedures required incisions of many inches. By minimizing the incision, the stress and loss of blood suffered by patients is reduced and the patients' recovery times are dramatically reduced.
Surgical trocars are most commonly used in laparoscopic surgery. Prior to use of the trocar, the surgeon will usually introduce a Veress needle into the patient's abdominal cavity. The Veress needle has a stylet which permits the introduction of gas into the abdominal cavity. After the Veress needle is properly inserted, it is connected to a gas source and the abdominal cavity is insufflated to an approximate abdominal pressure of 15 mm Hg. By insufflating the abdominal cavity, pneumoperitoneum is created separating the wall of the body cavity from the internal organs.
A trocar is then used to puncture the body cavity. The piercing tip or obturator of the trocar is inserted through the cannula or sheath and the cannula partially enters the body cavity through the incision made by the trocar. The obturator can then be removed from the cannula and an elongated endoscope or camera may be inserted through the cannula to view the body cavity, or surgical instruments may be inserted to perform ligations or other procedures.
A great deal of force is often required to cause the obturator to pierce the wall of the body cavity. When the piercing tip breaks through the cavity wall, resistance to penetration ceases and the tip may reach internal organs or blood vessels, with resultant lacerations and potentially serious injury. The creation of the pneumoperitoneum provides some free space within which the surgeon may stop the penetration of the trocar. To provide further protection, trocars have more recently been developed with spring loaded shields surrounding the piercing tip of the obturator. Once the piercing tip of the obturator has completely pierced the body cavity wall, the resistance of the tissue to the spring loaded shield is reduced and the shield springs forward into the body cavity and covers the piercing tip. The shield thereby protects internal body organs and blood vessels from incidental contact with the piercing tip and resultant injury. Trocars including various safety shield designs are described in Yoon, U.S. Pat. No. 4,535,773; Moll, U.S. Pat. No. 4,654,030; and Moll, U.S. Pat. No. 4,601,710. An improved piercing tip comprised of a pointed planar blade with an improved safety shield is also the subject of commonly owned U.S. Pat. Nos. 5,364,372 and 5,607,440.
Once the cannula has been introduced into the opening in the body cavity wall, the pneumoperitoneum may be maintained by introducing gas into the abdominal cavity through the cannula. Various seals and valves have been utilized to allow abdominal pressure to be maintained in this fashion. Maintaining abdominal pressure is important both to allow working room in the body cavity for instruments introduced through the cannula, and to provide free space for the puncturing of the body cavity wall by one or more additional trocars as may be required for some procedures.
While the existing planar bladed obturators and cannulas have proven useful, several disadvantages remain. For instance, it is desirable to reduce the force required to cause the piercing tip to penetrate a body cavity wall. Accordingly, designs that minimize the obstacles to penetration of the cannula through the body cavity wall are preferred. In addition, some existing shield mechanisms do not spring forward to cover the obturator tip as quickly as possible and it is necessary that the movement of the shield mechanism not create "pinch points" that could bind with body tissue.
Also, with the current emphasis on cost controls in health care, it is desirable to minimize the cost of medical instruments whenever possible. It has been expensive to manufacture previous flat bladed obturators due to the mounting of the blade in a metal hypotube sheath. Therefore, a need exists for an improved and less expensive apparatus for performing laparoscopic and similar surgical procedures.